New radio high swrs

Put in a new,actually this radio was my spare radio when I was otr now I'm doing just three states,radio and I can't get the swrs down no matter what I do.Changed coax,antenna,antenna mount ,cleaned ground and adjusted angle that the antenna was pointing.antenna is Wilson 1000 was a fire stick ,tried a Francis all have 3.5 or higher swrs. what's next.Truck is a Mack.got a Wilson 2000 still on my Pete may try that.radio is a uniden pc78 that ole Swamp dog,outside Memphis, has done some work on.

When your SWR reading is in the 3's or higher and tuning has no effect upon the reading, your problem is almost always an antenna ground plane problem. We are not talking about electrical grounding. What you need to look into is called "Bonding". Bonding is interconnecting the large metal components of the truck into one large ground plane for RF [radio frequency] purposes.
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Using a volt ohm meter [multimeter] on the lowest resistance scale, check the resistance between the antenna mount and a bare metal bolt on the door. The reading should be zero. If not, run a short ground strap from the antenna mount to the door.
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Next, check the resistance from the antenna mount to a bolt that mounts the door hinge to the cab. This should also be zero. If not, run a ground strap from the bolt that mounts the door to the hinge over to the bolt that mounts the hinge to the cab.
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Keep the ground straps short in length. Do not run a ground strap directly to the chassis frame because long wires can act like another antenna.

I would agree with all the Xcis has told you, you don't often hear that kind of common sense knowledge about antennas on the internet. All I would ad is make sure that all you connections are making contact with clean bare metal. And always break up the ground runs with heavy metal mass this like Xcis suggested you is to upset the Velocity factor so that it don't become a tuned circuit.. And use Heavy wire like 8 gauge fine stranded you need allot of metal mass for RF grounds.. Good Luck Oh one more thing the next time you check SWR's check on 1, 20 and 40 and take note on what the difference is if any. What you like see in these is a much different reading on 40 and 1..